38 METHODS FOR THE ANALYSIS OF URINE 



cloudy solutions or suspensions, the instrument thus modified 

 being called a nephelometer. In this later form of colorimeter 

 the depths of the colored solutions through which the light passes 

 are regulated by raising or lowering the cups and are accurately 

 indicated in millimeters on a vernier scale at the back of the instru- 

 ment. The standard solution is placed at any convenient depth 

 and the color of the solution to be examined is matched with it 

 by raising or lowering cups. When the color is of the same 

 intensity as the standard the depth of the solution is read. The 

 amounts of the colored substance in solution are inversely pro- 

 portional to the depths of the columns of fluid. Thus if the 

 standard is set at 10 mm. and the solution under examination 

 has the same color density at 20 mm. the latter has just one-half 

 the concentration of the standard. 



A large number of other colorimeters have been devised and 

 may be used in place of the Duboscq. Most of these though 

 less expensive than this instrument are also less accurate. The 

 Hellige colorimeter has been recommended, particularly for clin- 

 ical determinations by Myers and Fine. A simple colorimeter, 

 costing only about one dollar, has been devised and used with 

 considerable success by Peebles and Lewis. It is claimed to com- 

 pare favorably in accuracy with other colorimeters and to be 

 applicable to clinical and student use. Another accurate colorim- 

 eter has been developed by Bock and Benedict in which the 

 place of costly and difficultly obtainable prisms is taken by mirrors. 

 Kober has devised a combined colorimeter and nephelometer 

 which may be obtained in this country. For merely approxi- 

 mate determinations the color comparisons may be made directly 

 with a series of colored standards of varying strengths made up 

 in exactly similar test-tubes or small flasks. 



UREA 



Urease Methods 



Principle. These methods depend upon the principle that 

 the enzyme urease is able, at ordinary temperature, to transform 

 urea, quickly and completely, into ammonium carbonate. Take- 

 uchi in 1909 discovered the presence of this enzyme in the soja 

 or soy bean. The application of this enzyme to the determi- 



